The present invention relates to integrated circuit devices and methods of forming the same, and more particularly, to integrated circuit devices including storage capacitors and methods of forming the same.
A DRAM memory device typically includes a memory cell array and peripheral circuitry. A memory cell array is an assembly of memory cells that store data. Peripheral circuitry delivers data outside the DRAM device. A memory cell of a DRAM memory device includes one or more transistors and one or more capacitors. A transistor serves as a switch and a capacitor stores data. An important characteristic of DRAM memory devices is the capacitance of the memory cell capacitor which stores data. As such, methods of integrating capacitors with increased capacitance in smaller areas have become an important technology in DRAMs.
Design rules have become smaller as DRAM devices continue to be scaled down. In some instances, a “bridge” may occur between bottom electrodes (storage electrodes) of each cell, for example, due to misalignment during processing and/or smaller processing margins. The bridge may result in a defect called twin bit or multi-bit failure. More particularly, occurrence of the bridge problem in a stacked cell structure may be inversely proportional to the distance between the bottom electrodes. In other words, the occurrence of bridges may decrease as the distance between the bottom electrodes increases. However, as the usable surface area of the bottom electrodes decreases, the capacitance of the capacitor may also decrease.
A concave structure has been introduced that may address the above problem. A method of forming the concave structure may include forming a mold layer on a semiconductor substrate, etching the mold layer to form a bottom electrode hole, filling a bottom electrode material in the bottom electrode hole, planarizing the material to isolate the bottom electrodes for each cell, and removing the mold layer to expose the bottom electrodes. Other methods of forming the concave structure may include filling the contact hole with the bottom electrode material to form a box shape, or forming the bottom electrode material only on the internal wall of the contact hole to form a cylinder shape.
The bottom electrode may be formed to have a larger length or height compared to its width, in order to increase capacitance of the capacitor in a limited area. As a result, when the mold layer is removed and the bottom electrode is exposed, a bottom electrode with a high aspect ratio may collapse. Thus, a bridge between the bottom electrodes may occur.